1. Field of the Invention
The present invention relates to an ignition coil for an internal combustion engine to make a sparkling discharge on a ignition plug of the internal combustion engine such as a vehicle engine.
2. Description of Related Art
FIG. 6 shows a cross sectional view of a conventional ignition coil of an internal combustion engine disclosed in Japanese Utility Model Registration No. 3039423.
In the drawing there are shown an iron core 1 forming closed magnetic circuit, a gap 1a formed in the closed magnetic circuit, an actuated magnetic portion 1b of the iron core around which an primary coil 2 and secondary coil 3 are wound and the axis line 1c of the actuated magnetic portion of the iron core. The primary coil 2 is wound around a primary bobbin 2a and aligned. The secondary coil 3 also wound around a secondary bobbin (not shown) and aligned.
An switching unit 4 is disposed in parallel with the actuated magnetic portion 1b and provided with switching element 4a such as bipolar transistor and IGBT or the like. The primary coil 2 and a terminal 5a of a connector 5 are connected electrically one another with a conductor 6. A high voltage tower 7 outputs an electrical high voltage generated at the secondary coil 3. After the above described elements are disposed in a case 8, they are hardened stiffly in an oven together being immersed in vacuum by injection of a resin 9 through an opening 8a of case 8.
FIG. 7 shows a preferred embodiment of the ignition coil, described in FIG. 6, mounted to the internal combustion engine.
The drawing shows ignition coil 10 described in FIG. 6, the internal combustion engine 11, the ignition plug 11a, an axis line 11b of the ignition plug corresponding to the direction of screwing the ignition plug into the internal combustion engine and an adapter 10a connected to the ignition coil 10 wherein it is provided with conductor 10b inside and connects a ignition plug 11a with ignition coil 10 disposed inside a plug hole 11c. The ignition coil 10 is disposed at the top of the ignition plug of each cylinder lid wherein the axis line 1c of the actuated magnetic portion of the iron core and an axis line 11b of the ignition plug are perpendicular to each other.
For example, in the case where, as DOHC engine shown in FIG. 8, the ignition coil 10 is mounted in a narrow gap between the projections of the cam shield 50 used for the suction and exhaust, the switching unit 4 is disposed at the top of the actuated magnetic portion 1b being parallel to the axis line 1c of the actuated magnetic portion as shown in FIG. 9. The total width of the ignition coil may be minimized into minimum dimension LW excluding the dimension of the switching unit 4.
In case of mounting the ignition coil 10 to the internal combustion engine of the vehicle of which the hood 51 is low, as shown in FIG. 10, the total height of the IG coil needs to be decreased. As shown in FIG. 11 the switching unit 4 is disposed at the opposite side against the corresponding surface 1d of the iron core, sandwiching the activated magnetic portion 1b, being parallel to the axis line 1c of the activated magnetic portion. By this way the total hight of the ignition coil may be minimized into minimum dimension LH excluding the dimension of the switching unit 4.
The motion of the ignition coil will be described according to the FIG. 12.
Synchronizing to the ON OFF motion of the ignition signal generated from an engine control unit 20, the switching element 4a repeats the ON and OFF of the primary current to the primary coil 2. When the primary current starts to flow, the current is not dashed but increased in the form of chopping waves proportional to the time of the current flow by an inductance of a magnetic circuit and the primary current is intercepted instantly by the OFF motion of the ignition signal. In the primary coil 2 an electromotive force is generated at the interception of the primary current. In the secondary coil 3, a high voltage is generated proportional to the multiple number of the turns of both the primary coil 2 and the secondary coil 3, this high voltage is supplied to the ignition plug 11a through the high voltage tower 7 and the adapter conductor 10b. 
A center electrode supplied the high voltage from the ignition coil and a side electrode connected to the earth are disposed at the top end of the ignition plug 11a and begins the discharge electricity when the air mixture of the fuel between the electrodes caused an isolation breakage by the supplied high voltage. This discharge is called the inductive discharge. The energy supplied from the primary coil of the ignition coil is injected in a mixed air in each cylinder of the internal combustion engine and forms the firing source in the discharge channel and grows it and finally sets fire to the fuel. The output voltage and energy of the ignition coil are almost proportional to the interception current value of the primary current, therefor in result it is proportional to the flowing time of the electricity.
In the process of being converted to the magnetic energy of the iron core, the energy supplied from the primary coil 2 is limited by the magnetic flux saturation of the iron core 1. The maximum magnetic flux density of the iron core 1 is xe2x80x9cmagnetic flux density of the magnetic material used for the iron core for instance silicon steel plate etc.xe2x80x9dxc3x97xe2x80x9can area of the iron core section.xe2x80x9d At the present time the required energy for the engine not requiring the large output energy of the ignition coil especially is about 23 mJ and as for the lean burn engine which appears in recent years and the engine which emits a jet inside the cylinder, the required energy is about 45 mJ. As the result of examining it based upon the iron core used for the ignition coil, it is recognized that required section area of the iron core of the actuated magnetic portion is more than 50 mm2. This area may realize the energy of more than 23 mJ.
Disposing the magnet in the gap with the polarity having an opposite magnetic direction against the actuated magnetic direction of the primary coil and using it from the condition in which the iron core is saturated in the magnetic field having opposite direction against the actuated magnetic direction, the energy accumulated in the magnetic circuit becomes twice as much. This method may realize the energy of about 45 mJ.
Object of the Invention
One of the main elements defining the length of the ignition coil axis direction is the turning length of the primary coil. It corresponds to the dimension L0 in FIG. 6. For example in the prior art, the primary coil 2 wound by 150T having the maximum finished outside dimension is about 0.5 mm. In a primary bobbin 2a the coil should be a multiple layer like double layers or four layers because the starting position and the ending one of the coil should be coincides with each other. In the prior art the ignition coil has double layer and the length L0 of the winding wire is 0.55 mmxc3x97(150T/2 layer)=37.5 mm. As the length L1 of the case is about 45 mm, it is recognized that about 90% of it are the dimension of the primary coil.
The cylinder span Lk (FIG. 7) of the internal combustion engine of around 1500 cc vehicle is about 90 mm, therefor in the case of mounting the conventional ignition coil shown in FIG. 6 at the condition shown in FIG. 7, considering:
Case length L1+dimension to mount the iron core L2: 16 mm+connector dimension length L3: 22 mm+allowance of the dimension for insertion and removal: 10 mm, it is recognized that there is no more space.
If we design the ignition coil acceptable for the cylinder span LK of about 105 mm based upon the consideration of a big cylinder span engine, it is necessary to keep the case length L1 within 60 mm.
The small diameter of the primary coil will bring a short winding wire length L0, but the resistance value of the primary coil will increase. In the case of where the voltage of the battery is low at the start of the internal combustion engine, the resistance limits the primary current. Because of the above-described reason enough interception current is not prepared to get the necessary characteristics. Therefor the best diameter of the primary coil exists.
In the system of the individual ignition disposing the ignition coil at the top of the ignition plug of each cylinder, the axis direction length of the ignition coil is limited because of the limitation of the cylinder span of the internal combustion engine. In the case of using the ignition coil which includes the switching unit 4 within it, the position should be kept parallel to the axis line 1c of the actuated magnetic portion 1b of the iron core.
In the conventional product the switching unit 4 including the switching element 4a inside it and the axis line 1c of the actuated magnetic portion 1b of the iron core are disposed in parallel each other therefore we had to prepare two kinds of product to dispose the switching unit 4 at the suitable position for both the case of internal combustion engine layout requiring the shortening the total width LW of the ignition coil as shown in FIG. 8 and the case of internal combustion engine layout requiring the decreasing the total height LH of the ignition coil shown in FIG. 10. In near future when the kinds of the product are increased we have to increase the press mold for the case and investment for the equipment corresponding to the many kinds of product. It is the great disadvantage for the production cost.
The object of the present invention is the improvement of the above disadvantage. We can apply only one type of the ignition coil for both the case of internal combustion engine layout requiring the shortening the total width of the ignition coil and the case of internal combustion engine layout requiring the decreasing the total height of the ignition coil. Furthermore we submit the product enable to mount it in a severe layout of the internal combustion engine which is limited both for the height and the width. As the result it is the object of the present invention to get the ignition coil for the internal combustion engine which is enable to reduce the cost greatly by reducing the kind of the press mold for the case and investment for the equipment by reducing the kinds of products, and reducing the labor cost for the production process and increase the production quantity for the each equipment.
xe2x80x9cAn ignition coil for an internal combustion engine according to a first embodiment of the invention includes: an actuated magnetic portion of an iron core which has an axis line crossing an ignition plug axis line of the internal combustion engine at a right angle and around which a primary coil is wound; and a switching unit which is disposed at an end of the actuated magnetic portion vertically to the axis line of the actuated magnetic portion and flows and intercepts a primary current flowing through the primary coil.xe2x80x9d
xe2x80x9cThe ignition coil for an internal combustion engine according to this embodiment of the invention further comprises a cross section area of the iron core being 50 mm2 or larger.xe2x80x9d
xe2x80x9cThe ignition coil for an internal combustion engine according to the first embodiment of the invention further comprises a case that has the actuated magnetic portion and the switching unit built-in, in which a length of the case in an axis line direction of the actuated magnetic portion is shorter than 60 mm2.xe2x80x9d
xe2x80x9cThe ignition coil for an internal combustion engine according to the first embodiment of the invention has an iron core made of a magnetic steel plate having direction characteristics in the axis line direction of the actuated magnetic portion the actuated magnetic portion.xe2x80x9d
xe2x80x9cThe ignition coil for an internal combustion engine according to the first embodiment has a switching element in the switching unit that intercepts a current at 7.5A or larger.xe2x80x9d
xe2x80x9cThe ignition coil for an internal combustion engine according to the first embodiment of the invention has an iron core which is a closed magnetic circuit iron core having a gap.xe2x80x9d
xe2x80x9cThe ignition coil for an internal combustion engine according to the first embodiment of the invention has an iron core made of a closed magnetic circuit iron core having a gap, in which the gap of the closed magnetic circuit iron core is formed outside of the actuated magnetic portion.xe2x80x9d
xe2x80x9cThe ignition coil for an internal combustion engine according to the first embodiment of the invention further comprises a side iron core portion which is connected to the actuated magnetic portion at a part of the closed magnetic circuit iron core and is disposed between the actuated magnetic portion and the switching unit. This side iron core portion has a cross section that is almost equal to that of the actuated magnetic portion, in which a cross section shape of the side iron core portion is a rectangular shape having a shorter side extending in the direction of the axis line of the actuated magnetic portion.xe2x80x9d
xe2x80x9cThe ignition coil for an internal combustion engine according to a second embodiment of the invention includes: an actuated magnetic portion of an iron core which has an axis line crossing an ignition plug axis line of the internal combustion engine at a right angle and around which a primary coil is wound; and a switching unit which is disposed at an end of the actuated magnetic portion vertically to the axis line of the actuated magnetic portion and flows and intercepts a primary current flowing through the primary coil, in which the iron core is an open magnetic circuit iron core.xe2x80x9d